This application claims priority to Japanese application serial number 2000-382374, which application is hereby incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to power tools, and in particular to power tools that are driven by batteries, e.g., rechargeable batteries, as a power source. More particularly, the present invention relates to switches for operating a power tool motor driven by a battery power source.
2. Description of the Related Art
Known power tools are capable of being driven by either an AC power source or a DC power source. Generally speaking, rechargeable batteries have been used as the DC power source. In order to enable longtime continuous operation, some power tools that are driven by an AC power source (hereinafter called xe2x80x9cAC power toolsxe2x80x9d) have an ON lock mechanism for locking a motor switch in an ON position. The ON lock mechanism allows the power tool to be continuously operated without being required to hold the motor switch. However, power tools that are driven by batteries (hereinafter called xe2x80x9cDC power toolsxe2x80x9d) generally do not include an ON lock mechanism in order to (1) avoid wasteful discharge of the batteries and/or (2) prevent the power tool from being accidentally driven if the recharged batteries are mounted on or inserted into the power tool while the ON lock mechanism is in the ON position. In recent years, however, the quality of rechargeable batteries has considerably improved and rechargeable batteries now provide a relatively long usable time. Therefore, DC powered tools having ON lock mechanisms also have been proposed.
Such known battery powered tools with ON lock mechanisms have been designed such that the battery (or a battery pack) can be removed while the motor switch is still locked in the ON position. Further, known power tools have been designed to prevent the motor from being accidentally driven when the recharged batteries are again mounted on the tool.
For example, Japanese Utility Model Publication No. 3-18148 teaches a DC power tool that has an ON lock mechanism and an ON lock releasing mechanism. When the batteries have been discharged, the batteries are typically removed from the tool for recharging. During this removal step, the motor switch is held in the ON position by the ON lock mechanism. The ON lock releasing mechanism only releases the ON state of a motor switch when the recharged batteries are re-mounted on the tool.
However, because the known ON lock releasing mechanism releases the ON state only when the recharged batteries have been re-mounted, the motor switch is held ON after the discharged batteries have been removed. As a result, the operator may not be certain as to whether or not the ON lock releasing mechanism will reliably operate when the recharged batteries have been re-mounted. Therefore, the operator is sometimes required to manually turn OFF the motor switch before the recharged batteries are re-mounted, thereby making the known ON lock releasing mechanism inconvenient to use.
It is, accordingly, one object of the present invention to teach improved DC power tools. For example, in one aspect of the present teachings, the power tools may provide improved operability and convenience compared to known DC power tools.
In one embodiment of the present teachings, power tools may include a power source, e.g., a rechargeable battery, mounted on a tool body. A switch may be electrically connected to the battery in order to supply power to a motor that may be disposed within the tool body. An ON lock mechanism may serve to lock the switch in an ON position during operation of the power tool. The ON lock state of the switch preferably may be released (or the switch may be turned OFF) when the battery is removed from the power tool. More preferably, the switch is automatically (i.e., without operator assistance) released or turned OFF when the battery is removed from the power tool, e.g., for recharging.
Thus, when the operator removes the battery in order to recharge the battery, the switch may be automatically turned OFF. Therefore, the motor may be reliably prevented from being accidentally driven when the operator re-mounts the recharged battery on the power tool. Preferably, the power tool is designed so that the operator can visually recognize that the switch is turned OFF. As a result, the operability and convenience of the power tool can be improved and the operator can be certain that the motor will not be accidentally driven when the battery is re-mounted on the power tool.
Preferably, the ON lock mechanism prevents the switch from being locked in the ON position as long as the battery is not mounted on the power tool. Therefore, the switch can be reliably prevented from being set in the ON position when the battery is re-mounted on the power tool.
In another embodiment, the ON lock mechanism may include a detection rod that can change position in response to the presence or non-presence of the battery within a battery mounting space defined in the tool body. When the battery is set or mounted in the battery mounting space, the detection rod may be positioned in a first position, so that the detection rod can cooperate with a switch lever to lock the switch in the ON position. On the other hand, when the battery has been removed from the battery mounting space, the detection rod may automatically move from the first position to a second position. As a result, the ON lock state of the switch preferably will be released by such movement of the detection rod.
More preferably, the switch may automatically move to the OFF position as the detection rod moves to the second position. Therefore, if the detection rod is an element of the ON lock mechanism, the detection rod also may serve to release the ON lock state, so that the power tool may have a relatively simple design.
Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.